This invention relates to a cable testing system for determining open-circuit, short-circuit, and cross-over mapping between the wires of a cable, use being made of a far end unit connected with one end of the cable and operable between resistive and frequency signal modes, and a near end unit connected with the near end of the unit for determining open and short circuit conditions of the wires during the resistive mode, and for mapping cross-over between the wires during the frequency signal mode. In order to identify the wires, use is made of means for determining pulse width, cycle length and slope.